Stuck with "java.util.ConcurrentModificationException"

Question

Here is my code:

// eventList is a LinkedList public void run() { Iterator<Event> it = eventList.iterator(); int size = eventList.size(); while(size > 0) { while(it.hasNext()) { Event e = it.next(); //flaged line if(e.ready()) { System.out.println(e); e.action(); eventList.remove(e); --size; } } } } 

The error java.util.ConcurrentModificationException is thrown on the aligned flag ( Event e = it.next(); ). Do you see an error in my code that makes the reason for throwing this exception obvious?

Answer 1

You change eventList when using eventList.remove() , iterating over it. You must not do this, or the Iterator becomes unusable.

Just replace eventList.remove(e) with it.remove() and everything should be fine.

In addition, you can easily start an infinite loop if one of your events fails on the first run, because it.hasNext() will never return true after it returns false , but size can also not be changed. One solution would be to move the entire line of Iterator it = ... inside the first while .

I would also modify the outer while to use while (!e.isEmpty()) instead of manually tracking the size of the eventList .

Answer 2

You must delete the item through the iterator, otherwise the iterator will get reset because the base collection has changed.